Process for the treatment of oil-wax mixtures



May 11, 1937. J ALEXANDER 2,079,596

PROCESS FOR THE TREATMENT OF OIL-WAX MIXTURES Filed Jan. 30, 1935 2Sheets-Sheet l l 8500i 8 Solverzl 22 Diaplacemerzl 5 Tank Tani Z z'yaz'aTani I L C7zz'ller 3 10 24 4 X 29 M24249 7 4211? e; W5

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11 I zZs-placemeni 19 12 13 3B C /71'//er 16 fi avy flzykf Wax EffluxEff/ax Tank Tani Tank z/ FMQ h is AZZOTnegy May 11, 1937. J. A.ALEXANDER PROCESS FOR THE TREATMENT OF OIL-WAX MIXTURES Filed Jan. 50,1935 ZSheets-Sheet 2 Inventor- Joseph AAZex ander By 2min;

his Aiiorrze y Patented May 11, 1%37 STATES PATENT QFECE PROCESS FOR THETREATMENT OF OIL-WAX MIXTURES Application January 30, 1935, Serial No.4,158

5 Claims.

The present invention relates to an improved process for the separationof hydrocarbon oilwax mixtures and relates particularly to animprovement in the process disclosed in a co-pend- 5 ing application ofS. W. Ferris, Serial No. 4,157,

filed January 30, 1935.

Briefly, the process disclosed in the co-pending application of Ferrisconsists in preparing an oilwax mixture, for example, by distillation,which upon cooling to the desired separating temperature willcrystallize wax tothe extent of 10% or less of the total volume of themixture; or the dilution of a wax bearing stock with a suitable rsolvent, so that upon cooling to the desired separating temperature, waxwill crystallize to the extent of 10% or less of the total volume of themixture. The oil-wax mixture so prepared is then cooled to the desiredtemperature, with or without agitation, in such a manner as to effect adispersion of the wax crystals throughout the -mother liquor withreasonable uniformity. If agitation is resorted to, the cooled motherliquor containing the wax crystals is thereafter per mitted to stand,unagitated, for sufficient time to efiect the formation of a highlyporous wax mass, the structure of which has a certain degree ofmechanical strength, such mass containing less than substantially 10% ofsolid wax per unit volume of the mass. The displacement of the motherliquor from the cooled wax mass is then accomplished by passing adisplacing liquid, preferably an oil solvent, through the mass in such amanner that a substantially horizontal interface is maintained betweenthe mother liquor in the mass and the displacing liquid, thedisplacement pressure (difierential pressure or pressure drop throughthe wax mass) being of the order of 5 lbs/sq. in. or less, per footdepth of wax mass, and the concentration of crystalline wax being lessthan substantially 20% by volume of the mass in which mother liquor isstill present.

The displacement step is usually accompanied by the settling orcompacting of the wax mass from which the mother liquor is beingremoved, but such compacting is controlled to prevent the concentrationof crystalline wax in the mass from exceeding substantially 20% byvolume of the mass. This control is obtained by the proper adjustment ofthe quantity of wax crystallized from the mother liquor to form. theinitial wax mass, the rate and degree of cooling, the differentialpressure required for displacement and the gravity differentials betweenwax, mother liquor and displacing liquid. Upon completion of thedisplacement operation the solvents employed may be separated from theoil and wax fractions by distillation.

In carrying out the process, it is necessary to 60 control the quantityof wax in the mother liquor so that the crystalline wax content of themass resulting from the chilling of the mother liquor will not exceedsubstantially 10% of any unit Volume of the mass at the beginning of thedisplacement operation. In most instances, it has been found that thecrystalline wax contained in the wax mass at the beginning of thedisplacement step should be of the order of from 1% to 6% by volume, andpreferably of the order of from 2.5% to 4.5% by volume; it may, however,be as high as 10% by volume depending upon the character of the waxcrystals. Furthermore, in general, the differential pressure required ineffecting displacement does not exceed substantially 5 lbs/sq. in. perunit (1 foot) depth of the wax mass, and. usually at the outset does notexceed 2 lbs/sq. in. It is to be understood, however, that at some stageof the operation, and particularly during the latter part thereof, thepressure may be somewhat in excess of 5 lbs/sq. in. per 1 foot depth ofthe mass.

In the displacement process as above outlined, it has been customary toemploy a vertical, straight-walled cylindrical vessel for carrying outthe displacement of mother liquor from the crystalline wax mass, suchvessel being provided with heating and/ or cooling means, feed anddischarge connections and a screening means at the top or bottom of thevessel to prevent the escape of wax crystals, the position of suchscreening means depending upon the direction of flow, i. e., upward ordownward displacement.

It has been found, in some instances, that during the displacement ofmother liquor from the wax mass contained in the aforementionedstraight-walled vessels, cracks or channels will appear in the mass orthe mass will contract from the walls of the vessel leaving an annularchannel thru which washing liquid is prone to flow, thus rendering thedisplacement and washing operation very inefficient. The formation ofcracks or channels is highly undesirable, inasmuch as the displacing orwashing liquid will tend to flow thru the paths of least resistance, i.e., the cracks or channels, with the result that considerable quantitiesof mother liquor will remain in those portions of the wax mass thusbypassed.

I have discovered. that such difficulties may be obviated to a greatextent by employing a vessel having sloped or tapered walls, preferablya jacketed vessel of truncated conical shape. During the step ofdisplacing the mother liquor from the wax contained in such a taperedvessel, that portion of the mass in which the mother liquor has beenreplaced by displacing liquid tends to settle or compact in a verticaldirection and simultaneously in a horizontal direction due to theprogressively decreasing diameter of the vessel. The horizontalcompacting thus obtained prevents the formation of cracks or channelsduring displacement and permits a more uniform and efiicient removal ofmother liquor from the wax mass.

For purposes of illustration, reference is made to the accompanyingdrawings in which Fig. 1 represents diagrammatically, apparatus suitablefor carrying on my process; and Figs. 2, 3, and 4 representmodifications of my displacement vessel.

Referring to Fig. 1:

From a steam jacketed stock tank I, 40 parts, for example, of awax-bearing distillate from East Texas crude oil having a pour test of125 F., and a Saybolt universal viscosity of 60 seconds at 210 F., iswithdrawn through valvecontrolled pipe 2 and pumped by pump 3 throughvalve-controlled pipe 4 into mixing tank 5 provided with heating coil 6and stirrer I. Simultaneously or subsequently 60 parts, for example, ofethylene dichloride is withdrawn from solvent tank 8 by means ofvalve-con trolled pipe 9 and pumped by pump I0 through valve-controlledpipe i into mixing tank 5. Herein the solvent and distillate containingwax is agitated at a temperature of, for example, 120 F., until ahomogeneous solution is obtained. The resulting solution is passed fromthe mixing tank 5 by means of valve-controlled pipe II and is pumped bypump I2 thru valve controlled pipe I 3 to chilling device I 4, whereinthe solution is cooled until the temperature is of the order of, forexample, F., and a portion of the wax has crystallized. Thisoi1-waxsolvent mixture is passed from the chilling device I4 throughValve-controlled pipe I5 into the brine-jacketed displacement tower I6above the screen I'I. Prior to the introduction of the chilled mixtureinto the tower I6, air pressure is applied to brine tank I8 throughvalve-controlled pipe I 9 provided with valved vent I9a, and brine isforced through valve-controlled pipe 2 and pipe 2I into the conicallower section of tower I5 until it barely covers the screen IT. Thebrine and screen I I thus support the chilled oil-wax-solvent mixture inthe tower I6. The mixture contained in the displacement tower I6 is thencooled at a rate of, for example, from 1 F. to 4 F., per hour, until thetemperature of the mixture is of the order of, for example, 65 F., andthe desired final quantity of wax has crystallized out. The cooling inthe tower I6 may be efiected by circulation of cold brine in the towerjacket and/or by the employment of brine coils or pipes (not shown)installed within the tower.

The mixture is preferably allowed to remain in a quiescent state withintower I6 during the final cooling period, in which time the wax crystalsform an agglomerate mass of appreciable mechanical strength while stillretaining a high degree of free space or porosity thruout wlL'ch themother liquor is distributed. At the completion of the cooling period,parts of a displacing liquid, for example, naphtha of 50 A. P. I.gravity, is passed from the displacement liquid tank 22 throughvalve-controlled pipe 23, cooled to about 65 F. in cooling coil 24 andintroduced into the displacement tower It by means of valve-controlledpipe 25, above the surface of the chilled oil-wax-solvent mixturecontained therein. The displacing liquid is introduced in such a manneras to prevent substantial disturbance of the wax mass from which the oiland solvent are to be displaced. Preferably simultaneously with theintroduction of the displacing liquid at the top of tower I 6, brine iswithdrawn from the bottom of said tower and returned to the brine tankI8 by means of valve-controlled pipe 20. Oil and solvent from the waxmass, displaced downwardly by the incoming displacing liquid, iswithdrawn from the bottom of tower I6 and passed throughvalve-controlled pipes 26 and 2! into receiving or heavy efilux tank 28.If necessary, slight pressure may be applied to the tower I6, above thelevel of its contents, by means of valvecontrolled air line 29 providedwith valved vent 30. The differential or displacement pressure shouldpreferably be maintained at less than 5 lbs/sq. in. per 1 foot depth ofthe wax mass, in order to prevent undue compacting of the wax crystals.When substantially all of the oil and solvent (heavy efllux) has beendisplaced from the wax mass into receiving tank 28, as evidenced by amarked change in gravity or other critical property of the liquidissuing from the tower IS, the hquid thereafter withdrawn from the toweris diverted into receiving or light efilux tank 3i by closingvalve-controlled pipe 2'! and opening valve-controlled pipe 32. Thislight efilux will consist primarily of displacing liquid containingresidual oil and solvent which has been washed from the wax mass. Thedisplacing or washing operation is preferably continued until theeflluent from tower I6 is principally displacing liquid.

At the completion of the displacing or washing operation, the wax masscontaining residual displacing liquid is forced upwardly and out oftower I6 through valve-controlled pipe 33 into wax receiving tank 3-4,by means of brine introduced into the bottom of the tower from brinetank I8. If necessary, the wax mass contained in tower It may berendered more fluid by the application of steam in the jacketsurrounding said tower. The heavy efilux (oil and solvent) in tank 23,the light efllux (oil, solvent and displacing liquid) in tank 3!, andthe wax containing residual displacing liquid may be withdrawn fromtheir respective receiving tanks by means of valve-controlled pipes 35,36 and 37 and passed to distilling apparatus (not shown), wherein thesolvent, i. e., ethylene dichloride, and the displacing liquid, i. e.,naphtha, may be separated and recovered from the oil and wax.

While, in the above instances, I have described the chilling of thesolution of oil stock and solvent from the mixing tank 5 as beingeffected partially within the chiller I4 and partially within thedisplacement tower I6, I may, if desired, pass the solution directly tothe tower by means of valve-controlled by-pass 38 and effect suchchilling entirely within the tower I6, or I may chill the solutionentirely in the chiller I l prior to the introduction thereof into thedisplacement tower I 6. The latter method of operation may be carriedout by pumping the heated solution directly from mixing vessel 5 throughvalve-controlled pipe I 3, chiller I l and valve-controlled pipe I5 intotower I B. In this instance, the chilled mixture is preferably allowedto remain in a quiescent state within tower I 6 for a period of, forexample, 4 hours, during which time the crystals form an agglomeratemass having appreciable mechanical strength while still retaining a highde ree of free space thruout which the mother liquor is distributed. Dueto the gravity differential between the wax and mother liquor a certainamount of upward settling of the former occurs, so that at the end ofthe quiescent period a lower layer of relatively wax-free oil solutionis present which may be about of the volume of the total charge. Thislayer is drawn off from the bottom, at the same time the wax masssettles until upon completion of the removal of the wax-free solutionthe bottom of the wax mass rests upon the screen. The displacement stepis then carried on as above described.

In place of the fully tapered vessel for downward displacement, shown inconnection with the above description, I may utilize the partiallytapered vessel illustrated by Fig. 2. The vessel (a) is surrounded witha heating or cooling jacket (b) and provided'with a displacing liquidinlet pipe (0), a stock charging inlet pipe (d), a screen and a brineinlet and outlet pipe (g) which is also employed as an outlet for motherliquor and displacing liquid.

The displacement vessels represented by Figs. 3 and l are suitable forupward, and upward or downward displacement, respectively.

In Fig. 3 the vessel ((1') is surrounded with a heating or coolingjacket (1)) and provided with a displacing liquid inlet pipe (0) a stockcharging inlet pipe (01'), a screen 0"), a brine inlet and outlet pipe(g) and an outlet pipe (h) for mother liquor and displacing liquid.

In Fig. 4 the vessel (a") is surrounded with a heating or cooling jacket(1)) and provided with screens (f). If such vessel is employed indownward displacement, stock is charged thrupipe (d) brine is introducedor withdrawn thru pipe (9"), mother liquor and displacing liquid arewithdrawn thru the same, and displacing liquid is introduced thru pipe(0"). If the same vessel is employed in upward displacement, stock ischarged thru pipe (12) brine is introduced or withdrawn thru pipe (57"),mother liquor and displacing liquid are withdrawn thru pipe (c") anddisplacing liquid is introduced thru pipe (i"). In all cases, the finalwashed wax may be withdrawn from either the top or bottom of the vesselsby means of the pipes shown. Furthermore, additional heating or coolingmeans, such as vertical pipes or coils (not shown) may be installedwithin the displacing vessels to aid in maintaining the desiredtemperature therein.

In the description of my process given hereinabove, I have shown thatethylene dichloride may be employed as the crystallizing solvent andnaphtha as the displacing liquid. In addition thereto, I may also employthe conventional dewaxing solvents such as acetone, acetone-benzol,alcohols, esters, ethers, halogenated hydrocarbons and liquefiednormally gaseous hydrocarbons.

For brevity, in the appended claims, the terms solvent liquid anddisplacing liquid are to be understood to comprehend those compounds inwhich oil is readily miscible and wax is relatively immiscible at thetemperatures employed in the separation of the oil and wax. Also, theterm wax mass as employed herein and in the appended claims comprehendsa porous mass or body of wax crystals containing oil or oil and solventdistributed therethrough.

What I claim is:

1. The process of separating a hydrocarbon oilwax mixture into oil andwax fractions containing less wax and oil respectively than saidmixture,

which comprises producing a wax-containing mixture, cooling said mixtureto effect crystallization of wax therefrom and to cause the formation,in a displacement zone of a diameter decreasing in the direction ofdisplacement flow, of a wax mass containing less than substantially 10%by volume of crystalline wax and displacing from said wax mass, withoutsubstantial agitation thereof and under a relatively low differentialpressure, the liquid constituents of said mass with a displacing liquid.

2. The process of separating a hydrocarbon oil-wax mixture into oil andwax fractions containing less wax and oil respectively than saidmixture, which comprises producing a wax-containing mixture, coolingsaid mixture to effect crystallization of wax therefrom in an amountless than about 10% by volume of said mixture, passing the cooledmixture into a displacing zone of a diameter decreasing in the directionof displacement flow, and displacing from said cooled mixture, withoutsubstantial agitation thereof and under a relatively low differentialpressure, the liquid constituents of said mixture with a displacingliquid.

3. The process of separating a hydrocarbon oilwax mixture into oil andwax fractions containing less wax and oil respectively than saidmixture, which comprises producing a wax-containing mixture, partiallycooling said mixture to crystallize therefrom a portion of the wax,passing the cooled mixture into a displacing zone of a diameterdecreasing in the direction of displacement flow, further cooling themixture to form a wax mass containing less than substantially 10% byvolume of crystalline wax and displacing from said wax mass, withoutsubstantial agitation thereof and under a relatively low differentialpressure, the liquid constituents of said mass with a displacing liquid.

4. The process of separating a hydrocarbon oil-wax mixture into oil andwax fractions containing less wax and oil respectively than saidmixture, which comprises diluting said mixture with a solvent liquid,cooling said diluted mixture to effect crystallization of wax therefromand to cause the formation, in a displacement zone of a diameterdecreasing in the direction of displacement flow, of a wax masscontaining less than substantially 10% by volume of crystalline wax anddisplacing from said wax mass, without substantial agitation thereof andunder a relatively low differential pressure, the liquid constituents ofsaid mass with a displacing liquid.

5. The process of separating a hydrocarbon oil-wax mixture into oil andwax fractions containing less wax and oil respectively than saidmixture, which comprises adding to said mixture a solvent liquid,heating such admixture to a temperature suflicientto effect solution,cooling the solution to effect crystallization of wax therefrom and tocause the formation, in a displacement zone of a diameter decreasing inthe direction of displacement flow, of a wax mass containing less thansubstantially 10% by volume of crystalline wax and displacing from saidwax mass, without substantial agitation thereof and under a relativelylow differential pressure, the liquid constituents of said mass with adisplacing liquid.

JOSEPH A. ALEXANDER.

